This sounds like a perfectly legal termination to me, but if you want to pursue this, talk to a labor law attorney who specializes in wrongful termination. I am sure you can find someone who will take your money. I am less sure that you can find someone who thinks you have a case.
Rehiring you (IMO) is a dangerous thing for the employer to do. That is one of the few things I can think of which might put some air in a wrongful termination case.
As far as suing for defamation, same answer. See an attorney who specializes in that. Neither issue are DIY, but are complex legal issues requiring attorneys who specialize in these things. 90% or so of all attorneys specialize in contract law, and would not understand a complex labor law issue if it walked up and piddled on their leg.
Lastly, employers are not courts of law and you are not Perry Mason. The employer is supposed to following the SH rules established by EEOC. It is perfectly legal to fire a completely innocent person because the rules say nothing about the employer establishing guilt or innocence. The rules say that all SH claims be taken seriously, and if there is a adequate reason to believe that the claim MIGHT be true, that the employer take some kind of action and that a similar offense has the same result for both a janitor and VP. This is very technical stuff and you need a qualified lawyer to have even a slight possibility of supporting a wrongful termination claim. Unless the employer rehires you and shoots themselves in the foot. Not a sure thing at that point, but employer would have just changed something simple into something complicated.

